Art of programming knuth pdf

Please forward this error screen to 158. English, interspersed with snippets of macros and traditional source art of programming knuth pdf, from which a compilable source code can be generated.

The main intention behind this approach was to treat program as a literature understandable to human beings. Donald Knuth since he believed that it was one of the few three-letter words of English that hadn’t already been applied to computer. However, it correctly resembles the complicated nature of software delicately pieced together from simple materials. Macros in a literate source file are simply title-like or explanatory phrases in a human language that describe human abstractions created while solving the programming problem, and hiding chunks of code or lower-level macros. The preprocessor also provides an ability to write out the content of the macros and to add to already created macros in any place in the text of the literate program source file, thereby disposing of the need to keep in mind the restrictions imposed by traditional programming languages or to interrupt the flow of thought. Knuth also claims that literate programming provides a first-rate documentation system, which is not an add-on, but is grown naturally in the process of exposition of one’s thoughts during a program’s creation.

The resulting documentation allows the author to restart his own thought processes at any later time, and allows other programmers to understand the construction of the program more easily. This differs from traditional documentation, in which a programmer is presented with source code that follows a compiler-imposed order, and must decipher the thought process behind the program from the code and its associated comments. The meta-language capabilities of literate programming are also claimed to facilitate thinking, giving a higher “bird’s eye view” of the code and increasing the number of concepts the mind can successfully retain and process. However, because these tools do not implement the “web of abstract concepts” hiding behind the system of natural-language macros, or provide an ability to change the order of the source code from a machine-imposed sequence to one convenient to the human mind, they cannot properly be called literate programming tools in the sense intended by Knuth. Weaving: Generating comprehensive document about program and its maintenance.

Weaving and Tangling are done on the same source so that they are consistent with each other. This example provides a good illustration of the basic elements of literate programming. The unraveling of the chunks can be done in any place in the literate program text file, not necessarily in the order they are sequenced in the enclosing chunk, but as is demanded by the logic reflected in the explanatory text that envelops the whole program. Macros are not the same as “section names” in standard documentation. In fact, macros can stand for any arbitrary chunk of code or other macros, and are thus more general than top-down or bottom-up “chunking”, or than subsectioning. The grand totals must be initialized to zero at the beginning of the program. C globals are automatically zeroed.

The documentation for a literate program is produced as part of writing the program. Instead of comments provided as side notes to source code a literate program contains the explanation of concepts on each level, with lower level concepts deferred to their appropriate place, which allows for better communication of thought. Such exposition of ideas creates the flow of thought that is like a literary work. TeX for typesetting of the documentation. Knuth had privately used a literate programming system called DOC as early as 1979. It is now being developed by Tim Daly, one of the developer of scratchpad, Axiom is totally written as a literate program.

It is well known for its simplicity, given the need of using only two text markup conventions and two tool invocations, and it allows for text formatting in HTML rather than going through the TeX system. Literate is a “modern literate programming system. Like noweb, it works with any programming language, but it produces pretty-printed and syntax-highlighted HTML, and it tries to retain all the advantages of CWEB, including output formatted like CWEB. Other notable advantages compared with older tools include being based on Markdown and generating well-formatted “tangled” code.

Like noweb, it is independent of the programming language of the source code. It also has extensive indexing and cross-referencing facilities including cross-references from the generated code back to the documentation, both as automatically generated comments and as strings that the code can use to report its behaviour. HTML” and “virtual views” on code. It uses “noweb” markup for the literate source files. Instead of the machine-readable source code being extracted out of the literate documentation sources, the literate documentation is extracted out of the normal machine-readable source code files.

This allows these source code files to be edited and maintained as usual. Codnar generates a linear narrative describing the code, similar to that created by classical LP tools. Codnar can co-exist with API documentation tools, allowing both a reference manual and a linear narrative to be generated from the same set of source code files. The code can be also marked in the Richard Bird style, starting each line with a greater than symbol and a space, preceding and ending the piece of code with blank lines. I had the feeling that top-down and bottom-up were opposing methodologies: one more suitable for program exposition and the other more suitable for program creation. But after gaining experience with WEB, I have come to realize that there is no need to choose once and for all between top-down and bottom-up, because a program is best thought of as a web instead of a tree.

A hierarchical structure is present, but the most important thing about a program is its structural relationships. May 1986 article by Jon Bentley and Donald Knuth in one of the classical Programming Pearls columns in Communications of the ACM, vol 29 num 5 on p. WEB’s macros are allowed to have at most one parameter. Again, I did this in the interests of simplicity, because I noticed that most applications of multiple parameters could in fact be reduced to the one-parameter case. For example, suppose that you want to define something like In other words, the name of one macro can usefully be a parameter to another macro. Not only has it enabled me to write and maintain programs faster and more reliably than ever before, and been one of my greatest sources of joy since the 1980s-it has actually been indispensable at times.

Some of my major programs, such as the MMIX meta-simulator, could not have been written with any other methodology that I’ve ever heard of. Literate programming is what you need to rise above the ordinary level of achievement. Another surprising thing that I learned while using WEB was that traditional programming languages had been causing me to write inferior programs, although I hadn’t realized what I was doing. My original idea was that WEB would be merely a tool for documentation, but I actually found that my WEB programs were better than the programs I had been writing in other languages. TANGLE is able to scramble everything up into the arrangement that a PASCAL compiler demands. WEB-written program much more readable than the same program written purely in PASCAL, even if the latter program is well commented.

I have learned from my recent experiences. I chose the name WEB partly because it was one of the few three-letter words of English that hadn’t already been applied to computers. But as time went on, I’ve become extremely pleased with the name, because I think that a complex piece of software is, indeed, best regarded as a web that has been delicately pieced together from simple materials. We understand a complicated system by understanding its simple parts, and by understanding the simple relations between those parts and their immediate neighbors. If we express a program as a web of ideas, we can emphasize its structural properties in a natural and satisfying way. Knuth recast it into the WEB idiom.

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